The present invention relates to polyolefin/clay nanocomposites, more particularly, to poly-xcex1-olefin/clay nanocomposites, and to a process for the preparation of the same.
The conventional process for preparing thermoplastic composite materials is either dry-blending polymers with filling materials or adding filling materials into a melt of polymers and then mixing them. The resulting materials are disadvantageous for non-uniform distribution of the filling materials in the polymer matrix, thus largely decreasing their strength compared to the polymers containing no filling materials.
By filling polymers with superfine inorganic compounds, the resulting composite materials can have largely improved properties, and however, when the filling materials have a particle size less than 0.1 micron, it is difficult to have the filling materials dispersed in nanometeric scales by using the conventional blending process and only a micro-dispersed composite material can be prepared for very large self-aggregating force among the particles caused by very large surface areas. On the other hand, polyolefin materials with high or ultrahigh molecular weight have excellent mechanical properties and their application fields are being gradually broadened, however, when they are modified with superfine inorganic materials, the outstanding problem encountered is large power consumption and non-uniformity of the resulting composite materials.
In order to effectively solve the problem in terms of uniform dispersion of filling materials within the polymer matrix, a novel process, i.e. in-situ polymerization-composition, is proposed, in which a component having catalytic activity is supported on filling materials having high dispersibility and the polymerization reaction is then carried out on the surface of the filling materials to obtain a composite material. For example, U.S. Pat. No. 5,352,732 disclosed a homogeneous composite comprising (a) 10 to 99.5% by weight of an ultrahigh molecular weight linear polyethylene having a molecular weight of at least about 400,000 and (b) 0.5 to 90% by weight of at least one inorganic filler compound having a neutral-to-acidic surface, said filler compound being an inorganic compound selected from the group consisting of alumina hydrates, silicas, calcium carbonate, hydroxyapatite, calcium hydrogen phosphate and clays. The composite of ""732 is prepared by supporting a transition metal as active ingredient onto the surface of the inorganic filler and then carrying out polymerization reaction on said surface. While the mechanical properties of said composite are improved to some extent, the manufacturing process is relatively complicated and the thermal treatment at high pressure is necessary after polymerization.
Chinese Patent Application Publication No. CN 1138593A discloses a polyamide/clay nanocomposite, prepared by intercalation polymerization method, in which a clay having cationic exchange capacity is mixed with a lactam monomer in the presence of a dispersing medium, the cationic exchange reaction and monomer intercalation reaction are carried out in the stabilized colloidal dispersion system formed with stirring at high speed, and then the lactam is polymerized by adding a catalyst, to obtain the composite. The clay used in the synthesis of said composite is montmorillonite.
An object of the present invention is to provide a polyolefin/clay nanocomposite, which has excellent mechanical properties and thermal resistance.
Another object of the present invention is to provide a process for the preparation of the polyolefin/clay nanocomposite according to the present invention, which is simpler compared to the processes employed in the prior art.
These and other objects, features and advantages of the present invention will be readily apparent to those skilled in the art from the following description taken in connection with the accompanying drawings.